Process for the manufacture of moistureproof opaque or transparent paper



Patented July 3, 1934 PATENT OFFICE,

rnooess son THE PARENT PAPER AOTURE or MANUF MOISTUREPROOF OPAQUE -RTRANS- Eugene Sonneni'eld, Paris, France in. Drawing. Application July20, 1932, Serial No. 623,687. In Germany July so, 1931,

. 8 Claims.

This invention relates to a process for the manufacture of moistureproofopaque or transparent paper.

A simple method of rendering paper moistureproof and transparent whichis very frequently employed is to impregnate the same with moltenparaflin, .wax or stearine or else oils.

Owing to their resistance to penetration by water, moisture and gasesand their adequate de- 10 gree of transparency, such oiled and waxedpapers find an extended application, which is limited only by the factthat they cannot easily be glued. Hard parafiln-papers are subjecthowever to the drawback that they crack even when bent to the slightestdegree so that transparency is of course, lost at the cracks, whilstflexible paraflin papers on the other hand, easily grease even whentouched with warm hands. Paraifined papers are moreover unsuitable forwrapping goods sen- 0 sitive to grease,particularly in tropical climatesor during warm seasons.

Another method of imparting the hereinbefore described qualities topaper is to apply a coating of transparent lacquer to one or bothsurfaces thereof. The transparency of these lacquered papers is greatlysuperior to that of parafllned papers and by selecting a suitablecomposition of the lacquer these coated papers can be rendered waterandmoisture-proof.

Such lacquered papers are however only superficially waterproof. Ifwater penetrates into the interior via the edges or from the back ofpaper coated on one side only, the paper becomes softened and thetensile strength is reduced considerably. Moreover moisture penetratesthrough the cracks or flaws in the waterproof coatingwhich are caused bythe excessively great difference between the flexibility and tensilestrength of the paper and the coating respectively and which cannot beremedied. The continuity of the waterproof coating is very easily brokenon subjecting the coatedpaper to stretching, bend-- ing and othermechanicalstresses during use,. with the result "that impermeability ofthe paper is lost at these places. Such coated paper 'therefore onlyaifords an apparent protection against penetration by moisture; theprotection being real only when rigid even surfaces are coated! such asfor example, maps and blackboards.

The present invention relates to the manufacture of both waterproof andmoistureproof paper; opaque or transparent, and aims at combining! theadvantageous qualities of the oiled (waxed) and lacquered papers withoutintroducing any of the disadvantages attending same.

According to the process of the present invention, rubber or oils, fatsand waxes of mineral, vegetable or animal origin and/or theirderivatives are worked up into plastic masses with cellulose estersand/or ethers and plasticizers which 00 are then incorporated in afinely divided condition with the paper-pulp before, during or aftergrinding it in the beating engine. The finely divided plastic materialin the paper-pulp con,- glomerates into a coherent mass when the paperis calendered on hot rolls, the framework of paper fibres beingcompletely embedded therein.

Paper manufactured by the process of the presentinvention is impermeableto water, moisture and gases, is transparent, does not grease and can bereadily glued or cemented. Its mechanical strength properties have beenmodified to such an extent that any coatings applied thereto if desiredfor improving the'transparency and producing a high lustre do not crack,even when the 76 paper is bent sharply.

The moistureproofing impregnating mass employed according to the presentinvention can be mixed with dyestuifs'and resins and if opacity isdesired, with pigments and other fillers.

Cellulose lacquers containing paraffin have already been recommended forwaterproofing purposes, but they are attended with the drawback, incontradistinction to the plastic masses of the present invention, ofbeing suitable only for producing a superficial layer, besides beingmuch more costly. No protection is therefore afforded to the interior ofthe paper against the action of water.

A proposal has already been made on the other hand, to, add celluloseesters to paper pulp prior to working up the pulp into paper orpasteboard, then to treat the finished paper with solvents adapted todissolve orgsoft'en the cellulose esters. After the evaporation of thesolvent "the fibres 96 are said to be cemented together by the dissolvedor softened cellulose ester, so that the paper has become waterproof andstronger.

Comparative experiments have shown that the aforesaidprocess is verydiflicult to carry out in 100 practice. Under the conditions requiredfor continuous manufacture the period of contact of the paper with thesolvent is too short, hence the cellulose esters contained in thepaperare only superficially softened, a coherent protective layer is notproduced and the resistance to tearing of the paper is not improved.Prolonged treatment of the paper with solvents extracts the cellulomesters out of the paper to a considerable extent. Moreover, the twosurfaces of the paper no ployed makes inevitably become tacky at thesame time. The method usedfor recovering the solvents emit difficult toforward the paper, tacky on both sides, with the necessary speed. It ismoreover, quite impossible to render paper with which has beenincorporated pure cellulose esters waterproof and moistureproof byhotcalendering, that is by the simple and economical method of the presentinvention, because cellulose esters, unless first gelatinized withcamphor substitutes, do not behave as plastic masses and consequentlycannot be fused under heat and pressure into an elastic coherent mass inwhich the framework of fibres is embedded.

The impregnating mass of the present invention is produced for exampleby'kneading cellulose esters or ethers in a jacketted kneading apparatuswith suitable quantities of plasticizers and a water repellent substanceas hereinbefore described; dyestuffs, resins, pigments and other fillersbeing incorporated if desired with the ad'- dition of small quantitiesof a volatile organic solvent or mixture of solvents. It is essentialduring this operation that the temperature should not rise above theboiling point of the :solvent employed. When the kneaded material isentirely homogeneous the temperature is increased so that the solvent isable to escape, the escaping solvent being replaced'by the same quantityof a precipitant of higher boiling point, such as for example, water. Assoon as the mass is free from solvent the temperature is increased againuntil the whole of the precipitant has been driven off.

The mass remaining is fritted together, de-' pending on the quantity ofplasticizers and water repellent substances employed, until it forms asoft paste, which cannot be converted into the fine state of subdivisionrequired for further treatment by the usual grinding ina mill. i

It has been ascertained in. accordance with the present invention thatthe required state of subdivision can be obtained in a very simplemanner by cooling the mass after the precipitant has beenexpelled-Imeading it constantly the while-down to the temperature ofordinary water, this temperature being maintained until the mass hasfallen to powder. The powder thus obtained is sifted and dried at roomtemperature. Any cellulose ester and ether can be employed for themanufacture of the impregnating mass, but it is preferable to employcellulose esters and ethers of high viscosity, in contradistinction tothe low viscosity esters and ethers used for cellulose lacquers, sincethe former produce more plastic masses which can more readily be workedinto the pores of the fibres when the paper is hot calendered. Moreovercellulose esters and ethers of high viscosity produce finished productsof improved mechanical. strength properties as regards stresses due tobinding or tension. A particularly suitable cellulose ether is ethylcellulose, due to its elasticity and softness.

Suitable plasticizers for the purpose of the present invention compriseall the substances and mixtures usually employed for cellulose ethersand esters, nevertheless the plasticizer mixture is advantageously ofsuchconstitution that it contains a preponderance of true gelatinizingagents for the cellulose esters and ethers employed, that is to sayagents which form with the latter so-called solid solutions which'do nottend to segregate under the action-of heat and pressure during the hotcalendering. It has moreover proved to be of advantage to select aplasticizing agent which simultaneously acts'as a solvent for variousother constituents of the impregnating mass, and especially for thewater repellent substances employed. Dibutyl phthalate, for example,fulfills. the aforesaid conditions if ethyl cellulose be employed forthe manufacture of the impregnating mass and if oils be employed forrepelling water. Highly satisfactory results accrue from the employmentof water soluble plasticizers of low volatility. Rubber, oils, fats andwaxes of mineral, vegetable or animal origin and derivatives thereof,

insoluble plasticizers may function simultaneously as water repellentagents.

The proportions in which the various ingredients are employed may varywithin wide limits depending on the requirements which the finishedproduct has to fulfill in respect of suppleness,

impermeability to moisture and transparency.

- The following composition of an impregnating mass of proved utility isgiven purely by way of example and is not intended to be limitative:

Percent Ethyl cellulose 65 Dibutyl phthalate 25 Castor oil 10 thereof.The mixture thus obtained is then precipitated as hereinbeforedescribed, finely divided and mixed up alone or with the addition offurther quantities of cellulose in the beating engine and worked up'intopaper as in the case of ordinary paper pulp.

Owing to the ready fusibility of this mass it is also possible toimpregnate the finished paperweb with sameusing small quantities of highboiling solvents if desired-similar to the method of impregnatingwithparaifin, for example.

It is advantageous in all cases to subject the impregnated paper web tohot calendering.

The proportion of impregnating mass to paper stock canbe varied' withinwide limits depending on the qualities desired in the finished product.Adequate impermeability to water is obtained, in the case of thin'paper,for example, by adding from 5 to -15% of the impregnating mass thereto.

I claimz-ie j '1. A proc: fss for the manufacture of moistureproofpaper-which comprises first gelatinizing a mixture of ulose derivatives,plasticizers, and water repellen ubstances, comminuting the plastic massso formed, and incorporating said plastic mass with paper pulp duringthe manufacture of paper therefrom.

2. A process for the manufacture of moistureproof paper which comprisesfirst gelatinizing a mixture of cellulose esters, plasticizers and waterrepellent substances, comminuting .the plastic mass so formed, andincorporating said plastic 4. A process for the manufacture ofmoistureproof paper which comprises kneading together cellulosederivatives, plasticizers and water repellent substances in the presenceof volatile organic solvents, at a temperature not in excess of theboiling point of said solvent, raising the temperature to expel thesolvent, precipitating the mass, cooling it to ordinary temperaturewhilst kneading continuously until the mass falls to powder, drying saidpowder and adding it to paper pulp mixing in a beating engine andworking the mixture up into paper.

to form a plastic mass, finely dividing said plastic mass andincorporatingit with paper pulp during the manufacture of papertherefrom.

6. A process for the manufacture of moistureproof paper which compriseskneading together cellulose derivatives, plasticizers, water repellentsubstances and tinctorial substances to form a plastic mass, finelydividing said plastic mass and incorporating it with paper pulp duringthe manufacture of paper therefrom.

7. A process for the manufacture of moistureproof paper which compriseskneading together cellulose derivatives, plasticizers, water repellentsubstances and pigments and other fillers to form a plastic mass, finelydividing said plastic mass and incorporating it with paper pulp duringthe manufacture of paper therefrom.

8. A process for the manufacture of moistureproof paper which compriseskneading together cellulose derivatives, plasticizers, and a wax-likemass to form a plastic mass, finely dividing said plastic mass andincorporating it with paper pulp during the manufacture of papertherefrom.

EUGENE SONNENFELD.

